Warning: You're about to cross over. Once you've tried games in virtual reality, it's going to be awfully difficult to go back to 2D gaming on a TV or monitor.

Better yet, you can enjoy some stellar VR experiences right away on your iPhone. This tends to surprise people, as Google Cardboard is the best-known driver of smartphone-powered VR and Google doesn't make iPhones.

But the reality is Apple's phones can work inside just about any Google Cardboard (or compatible) viewer. Now it's just a matter of finding the best VR games! Not into games? Check out my list of the 7 best VR apps for iPhone where you'll find virtual concerts, movies, even trips to the moon.

The App Store is all but exploding with cool new VR games. Below I've rounded up a selection of mostly-free virtual experiences you won't want to miss.

End Space VR

Screenshots really don't do End Space VR justice.

Screenshot by Rick Broida/CNET

Action and outer space seem like a perfect fit for VR, and End Space VR proves it. You're the fighter pilot, tasked with eliminating wave after wave of alien attackers. The action is fluid, the graphics beautiful. Ideally you'll pair your phone with a gamepad so you have a weapons trigger, but you can also rely on gaze-based aiming and shooting.

Fractal Combat X

Freemium jet-fighter Fractal Combat X is unique in that you can play it with or without a VR headset. If you want to use one, you'll need to enable the option in the Graphics settings menu -- either way, you will need a controller.

In this game, your head serves as the joystick: wherever you look, that's where your jet flies. Fractal Combat X offers impressive graphics and tons of RPG-style upgrade options for your jets and weapons. You can earn credits by playing, but you'll need to spend a few bucks if you want quick upgrades.

InCell VR

Dizzying and dazzling, InCell VR shrinks you down for a thrill ride inside a human body. Your goal is to eliminate viruses and save the host's cells from destruction. This is another game you can play with or without VR. If you use a headset, it'll be a good test of your ability to withstand motion sickness, but it's worth the risk. InCell VR is not some cobbled-together VR experiment; it's a fully formed and highly entertaining game. While you're at it, check out InMind VR from the same developer. Both games are free.

Lamper VR: Firefly Rescue

Lamper VR: Firefly Rescue, sequel to the classic Lamper VR, offers more of the same: an endless-runner gaming experience notable for great graphics and a decidedly kid-friendly motif. (You're a firefly, after all.) There's no game controller necessary: your head does all the steering.

Roller Coaster VR

Roller Coaster VR is the game (or simulation, anyway) you show your friends when you want to give them their first taste of VR. It's the chance to ride the kind of roller coaster that could never exist in real life, what with the rickety tracks built into the side of a mountain, the jumps, the water hazards, and more. A close second: Cedar Point VR, which takes you for a ride on the amusement park's real-world Valravn coaster. Dramamine not included.

Romans from Mars 360

Is it possible for a VR game to be adorable? It is when it's Romans from Mars, a sort of first-person tower-defense game that was already pretty cute in its non-VR version. Here you get to be up close and personal as you fight off wave after wave of invading Martians. And it's completely free, right down to the upgrades.

Zombie Shooter VR

In your face, zombies! (No, really, that's where you should shoot them.)

Screenshot by Rick Broida/CNET

Admit it: you've always thought you could do better than Rick Grimes and the gang on "The Walking Dead." In Zombie Shooter VR you get to prove your zombie-whompin' mettle as you mow down wave after wave of brain-thirsty walkers. Unlike most auto-shooters, this one puts you on foot, moving through tunnels, subway cars and other spooky environments. It's a first-person shooter on a rail -- a fairly easy one, but immensely satisfying for any fan of the undead.

Have you found any other must-have VR games for iOS? Name them in the comments!